1. Field of the Invention
The present invention generally relates to a data communication system, such as a local area network (LAN), and its access method, and, in particular, to a multichanneled multiaccess communication system.
2. Description of the Prior Art
In a bus type communications network, use is typically made of the so-called carrier sense multiple-access (CSMA) method for controlling an access to the network, and, in particular, use is often made of its modification of carrier sense multiple-access, collision detection (CSMA/CD) method, in which a multiple access is carried out while detecting a collision on the transmission line. In the CSMA/CD method, it is known that a relatively excellent performance can be obtained by a simple control; however, in the case where it is applied to a mono-channel architecture, the throughput deteriorates due to repeated collisions under heavy load condition, and, moreover, the delay characteristic becomes impaired thereby limiting the capacity of transmission line and the distance of communication.
For this reason, in order to improve the throughput and the delay characteristic, there has been proposed a modified CSMA/CD method of the distributed control type for use in a multi-channel architecture, which is called the Psi-net method and disclosed in the preprint of the Electronics and Communications Society published on Nov. 22, 1983. The proposed method adopts the distributed control format having a predetermined channel setting and it is so structured that a head end combines packets transmitted through transmitting channels and a receiving channel is constructed as a single channel of large capacity, whereby each station receives a single channel, and a receiver side is provided with a main channel for receiving each channel and a detecting channel for transmitting the transmitting channel as it is to the receiver side, whereby each station intrigues the detecting channel so as to carry out carrier detection and collision detection.
However, such a multiaccess communication means requires the provision of a head end which complicates the overall structure, and, at the same time, the transmission rate of the main channel must be increased as the transmission line capacity increases. For example, it can be easily put into practice if the transmission line capacity is in the order of 10 M bps, but if the transmission line capacity exceeds 100 M bps, the implementation of a transmitter/receiver for ultra high speed channel operation is extremely difficult.